1. Field of the Invention
The present invention relates to an automatic welding apparatus and more particularly to an automatic welding apparatus which can automatically move a welding torch along a welding line of plate-like welding workpieces.
In manufacturing machinery and tools it is often the case that plate-like members are welded together. For example, in a fluid tank provided with radiation fins, such as a casing for a transformer or the like, a corrugated radiation plate as shown in FIG. 1 of the attached drawings is used. In the example shown in FIG. 1 a metal sheet 1 having a thickness of about 1 mm is folded in a corrugated configuration at an interval A to form folded portions 2 at equal intervals, and each of the folded portions 2 has both its edge parts 2a and 2b pressed together, respectively, leaving a central portion 3 therebetween with the confronting portions of the metal sheet being extended outwards from each other, and the edge parts 2a and 2b are welded together, respectively, to form water tight seals. The metal sheet 1 thus shaped is used as e.g. the side walls of a liquid containing tank. However, when such a corrugated radiation plate is used in the contruction of a liquid containing tank, since the overall rigidity of the plate is insufficient for use as a tank wall, it is usual to weld to both edges of the plate 1 margin plates 4 and 5, each having a thickness of about 3 mm, respectively, to increase the overall rigidity, as shown in FIG. 2.
In practice, since one of the margin plates, the margin plate 4, is usually positioned at the top, its outer edge is bent with a curvature so as to form a rounded portion 4a over substantially the whole length, and on the rounded portion 4a is mounted a cover plate (not shown). The other of the margin plates, i.e. plate 5, has its outer edge bent at right angles so as to form a bent part 5a which is adapted to mount a bottom plate (not shown).
When the corrugated radiation plate 1 is to be stifferend by adopting such a construction as shown in FIG. 2, margin plates 4 and 5 and the corrugated radiation plate 1 are welded together with a lap joint having a predetermined lapping width of B, but since the end portions 2a and 2b of the folded portion 2 are formed by the bending of the metal sheet, it is often the case that a space 6 having a triangular shape is formed or an offset C is generated between the adjoining ends of the base portions 7 of folding portion 2 in the course of the shaping process. Further, since owing to internal residual stresses caused at the time of the shaping process the corrugated radiation plate 1 as a whole develops twists and warps, it has been impossible to weld the related joint portions between the corrugated radiation plate 1 and the margin plates 4 and 5 automatically by the use of an automatic welding machine. Therefore, it has been unavoidable that the actual welding has had to be carried out manually by a welding operator skilled in welding technique, yet without being able easily to ensure consistent welding quantity, and so poor productivity has resulted.